The present invention is applicable either to grand or to upright mechano-acoustic pianos having tone-generating elements in the form of struck strings made of steel core wire streched under tension. The strings may be either plain or wrapped with one or more layers of covering wire, each layer encircling the core wire in the form of a multi-turn helix. The piano usually has 88 notes, a key for each note, a hammer for each note and a compass spanning at least the frequency range from the note A0=27.5 Hz to the note C8=4186 Hz. It is the purpose of the invention to improve the tonal uniformity of the piano by eliminating or minimizing a tonal discontinuity common to many pianos. This defect is an undesirable difference in tonal amplitude and/or duration between the tones produced by playing adjacent piano keys. This usually occurs at certain natural scale "breaks" but may also occur within other small regions or groups of notes produced by adjacent keys or at certain natural scale "breaks". While not intended to be so limited, the invention will be described in terms of the elimination or minimization of a tonal discontinuity noticeable when playing adjacent keys which correspond to string locations on either side of the "bass break".
It is well known that the design of the soundboard and bridge structure of a piano is of primary importance in determining the tone quality of the instrument. However, the exact ways in which the soundboard and bridges influence tone quality often have not been fully understood. In the past it has sometimes happened that excellent results have been achieved as much from luck as from design, or that less than satisfactory results have been tolerated because the source of the trouble could not be identified. It has been found that modern digital electronic equipment and analysis techniques can contribute greatly to an understanding of the influence of soundboard construction upon the musical performance of the finished instrument. In the case of the present invention, attention was directed toward increasing the uniformity of tone quality of the notes on either side of the natural scale discontinuity usually referred to as the "bass break." The bass break is the demarcation between those notes whose strings are terminated vibrationally on the treble bridge and those notes whose strings are terminated vibrationally on the bass bridge. Again for purpose of an exemplary showing, the invention will be described in connection with an upright piano.
The use of small masses or weights in association with piano soundboards is not new in and of itself. For example, U.S. Pat. No. 486,013 teaches the use of a plurality of graduated weights affixed to a thick soundboard to increase its vibration. U.S. Pat. No. 962,393 describes improving the tone of pianos by affixing a pair of mushroom-shaped weights to the soundboard, the lighter one of the pair of weights being affixed to the soundboard back of the treble strings and the heavier one of the weights being affixed to the soundboard back of the bass strings.
The invention is based on the discovery that a tonal difference between the notes of adjacent keys, as at the bass break, can be minimized by the appropriate mounting of a small mass or weight on one of the soundboard bridges, as will be explained hereinafter.